Strain gauge method for measuring polymerization contraction of composite restoratives

Post-gel polymerization contraction of composite restoratives produces a volumetric change in phase with the development of a modulus of elasticity and distributes contractile stresses through the resin hard tissue interface into the tooth. A new method for monitoring the polymerization contraction of composite restoratives utilizes electrical resistance strain gauges. The strain gauge system was calibrated with dial gauge measurements of the bulk expansion of gypsum products. Three composite types (microfilled, hybrid and posterior) were evaluated for polymerization exotherm, contraction during curing, and contraction for various shades. A 60-s curing time was used. The posterior composite (P-50) demonstrated the lowest exotherm and polymerization contraction. The contraction for Silux Plus dark grey was significantly lower than all other shades of all materials. The strain gauge method appears to be well suited for real-time measurement of the curing process and provides a means for studying the kinetics of polymerization.